Optical Design with Zemax

Transcription

1 Optical Design with Zemax Lecture 9: Illumination Herbert Gross Summer term

2 2 Preliminary Schedule Introduction Properties of optical systems I Properties of optical systems II Aberrations I Aberrations II Optimization I Introduction, Zemax interface, menues, file handling, preferences, Editors, updates, windows, coordinates, System description, Component reversal, system insertion, scaling, 3D geometry, aperture, field, wavelength Diameters, stop and pupil, vignetting, Layouts, Materials, Glass catalogs, Raytrace, Ray fans and sampling, Footprints Types of surfaces, Aspheres, Gratings and diffractive surfaces, Gradient media, Cardinal elements, Lens properties, Imaging, magnification, paraxial approximation and modelling Representation of geometrical aberrations, Spot diagram, Transverse aberration diagrams, Aberration expansions, Primary aberrations, Wave aberrations, Zernike polynomials, Point spread function, Optical transfer function Principles of nonlinear optimization, Optimization in optical design, Global optimization methods, Solves and pickups, variables, Sensitivity of variables in optical systems Optimization II Systematic methods and optimization process, Starting points, Optimization in Zemax Imaging Fundamentals of Fourier optics, Physical optical image formation, Imaging in Zemax Illumination Advanced handling I Advanced handling II Correction I Correction II Physical optical modelling Introduction in illumination, Simple photometry of optical systems, Non-sequential raytrace, Illumination in Zemax Telecentricity, infinity object distance and afocal image, Local/global coordinates, Add fold mirror, Scale system, Make double pass, Vignetting, Diameter types, Ray aiming, Material index fit Report graphics, Universal plot, Slider, Visual optimization, IO of data, Multiconfiguration, Fiber coupling, Macro language, Lens catalogs Symmetry principle, Lens bending, Correcting spherical aberration, Coma, stop position, Astigmatism, Field flattening, Chromatical correction, Retrofocus and telephoto setup, Design method Field lenses, Stop position influence, Aspheres and higher orders, Principles of glass selection, Sensitivity of a system correction, Microscopic objective lens, Zoom system Gaussian beams, POP propagation, polarization raytrace, polarization transmission, polarization aberrations

3 3 Contents 1. Photometry 2. Illumination calculation 3. Light sources 4. Illumination systems 5. Special illumination components 6. Illumination in Zemax

4 4 Differential Flux Differential flux of power from a small area element das with normal direction n in a small solid angle dω along the direction s of detection d 2 L dwda S Lcosq SdWdA L dw sda S S da S q S s n dw Integration of the radiance over the area and the solid angle gives a power P da A

5 5 Transfer of Energy in Optical Systems General setup Radiation Source Optical System da S in out Detector da D P S P D da W 2 dw 2 q R P 1 da 1 Optical System W 1 2 Detector A r q 1 f d 2 Ref: B. Dörband

6 6 Illumination Fall-off Irradiance decreases in the image field Two reasons: 1. projection due to oblique ray bundles 2. enlarged distances along oblique chief rays Natural vignetting: smooth function depends on: 1. stop location 2. distortion correction y y p y' p y' E(y) axis bundle U w marginal ray chief ray off axis bundle chief ray R' Ex w' U' E(y') entrance pupil exit pupil

7 7 Natural Vignetting Consideration with the help of entrance and exit pupil: 1. transfer from source to entrance pupil 2. transfer between pupils 3. transfer from exit pupil into image plane da da AP EP n n' 2 da da' s s EP AP 2 cos cos 4 4 w w' object entrance pupil system exit pupil image marginal ray da EX q U w da EN w' U' q' da chief ray da' s p s' p

8 8 Natural Vignetting: System with Front Stop Exact integration: similar to general formula including differential magnification Special case on optical axis Approximation small aperture L da E'( w) da' da E' (0) L sin da' E' ( w) E'(0) cos 4 2 u w 4cos 2 w tan 1/ cos w tan u 2 u Special case circular symmetry da' h' dh m A da h dh' E L u k h 2 dh' 4 ' sin cos w f corr h' dh Appropriate distortion allows to correct the natural vignetting effect

9 Illumination Systems Special problems in the layout of illumination systems: 1. complex components: segmented, multi-path 2. special criteria for optimization: - homogeneity - efficiency 3. incoherent illumination: non-unique solution

10 10 Non-Sequential Raytrace: Examples 3. Illumination systems, here: - cylindrical pump-tube of a solid state laser - two flash lamps (A, B) with cooling flow tubes (C, D) - laser rod (E) with flow tube (F, G) - double-elliptical mirror for refocussing (H) Different ray paths H possible E: laser rod A: flash lamp gas B: glass tube of lamp C: water cooling F: water cooling G: glass tube of cooling 6 D: glass tube of cooling

11 Illumination Simulation Simple raytrace: S/N depends on the number of rays N N = N = N = N = Improved SNR: raytube propagation transport of energy density N TR = 63 N TR = 63 N TR = 63 N = N = N =

12 Realistic Light Source Models CAD model of light sources: 1. Real geometry and materials 2. Real radiance distributions Bulb lamp XBO- lamp

13 Gaussian Beam Propagation Paraxial transform of a beam Intensity I(x,z) 2P I( r, z) 2 w ( z) r 2 w( z) e 2 z intensity I [a.u.] x

14 Angle Indicatrix Hg-Lamp high Pressure Polar diagram of angle-dependent intensity Vertical line: Axis Anode - Cathode XBO- lamp cathode azimuth angles :

15 Spectral Distributions Xenon lamp Line spectrum 1 I I HG-Xe-lamp

16 Köhler Illumination Principle Principle of Köhler illumination: collector condenser objective lens Alternating beam paths of field and pupil No source structure in image Light source conjugated to system pupil source field stop aperture stop object plane back focal plane - pupil image plane Differences between ideal and real ray paths field stop filter aperture stop condenser collector source object plane

17 Illumination Optics: Collector Requirements and aspects: 1. Large collecting solid angle 2. Correction not critical 3. Thermal loading large 4. Mostly shell-structure for high NA a) axis W(y p ) b) field nm 546 nm 644 nm y p W(y p ) 200 y p a) axis W(y p ) b) field 200 W(y p ) 200 y p y p 480 nm 546 nm 644 nm

18 Illumination Optics: Condenser 2. Abbe type, achromatic, NA = 0.9, aplanatic, residual spherical a) axis b) field y' 100m tangential y' 100m sagittal x' 100m y p y p x p 480 nm 546 nm 644 nm 3. Aplanatic achromatic, NA = 0.85 a) axis b) field y' 100m tangential y' 100m sagittal x' 100m y p y p x p 480 nm 546 nm 644 nm

19 19 Fresnel Surfaces Special description of Fresnel surfaces with circular symmetry Bezier spline desciption with corresponding choice of the control points: modelling of edges Mathematically: - surface sag continuous - derivative with steps

20 Complex Geometries Lighthouse optics Fresnel lenses with height 3 m Separated segments

21 Illumination Components Solar concentrator optics Ref: Light Presciptions Innovations

22 Arrays - Illumination Systems Illumination LED lighting Ref: R. Völkel / FBH Berlin

23 Rectangular Integrator Slab Principle of a light pipe / slab integrator: Mixing of flipped profiles by overlapping of sub-apertures Spatial multiplexing, angles are preserved Number of internal reflexions determine the quality of homogeneity virtual intersection point length L point of incidence width a square rod exit surface

24 Rectangular Slab Integrator Ideal homogenization: incoherent light without interference Parameter: Length L, diameter d, numerical aperture angle q, reflectivity R Partial or full coherence: speckle and fine structure disturbs uniformity Simulation with pint ssource and lambert indicatrix or supergaussian profile x x' d q I(q) I(x') L

25 Rectangular Slab Integrator Full slab integrator: - total internal reflection, small loss - small limiting aperture - problems high quality of end faces - also usable in the UV slab integrator Hollow mirror slab: - cheaper - loss of 1-2% per reflection - large angles possible - no problems with high energy densities - not useful in the UV hollow integrator

26 Flyeye Array Homogenizer Array of lenslets divides the pupil in supabertures Every subaperture is imaged into the field plane Overlay of all contributions gives uniformity subaperture No. j u change of direction Problems with coherence: speckle x cent x ray Different geometries: square, hexagonal, triangles Simple setup with one array Darr f arr Improved solution with double array and additional imaging of the pupil D sub starting plane array condenser focal plane of the array receiver plane D sub D ill f arr f con

27 Flyeye Array Homogenizer Simple model: Secondary source of a pattern of point sources array condenser spherical surface with secondary source points illumination field

28 Segmented Surfaces and Arrays Types of surfaces: Mirror with facets Regular lenslet array Statistical lenslets Facettenspiegel einfallender Strahl bearbeitete Fläche

29 Flyeye Array Homogenizer Example illumination fields of a homogenized gaussian profile a) single array b) double array - sharper imaging of field edges - no remaining diffraction structures a b

30 Axicon Lens Combination Generation of a ring profile Axicon: cone surface with peak on axis Ringradisu in the focal plane of the lens Ro R ( n 1) f f Ring width due to diffraction R 1.22 f a a Ro f f

31 Illumination Optics: Condenser 2. Epi-illumination Complicated ring-shaped components around objective lens observation illumination ring lens circle 1 observation illumination object ring lens object circle 2

32 Illumination in Zemax Simple options: Relative illumination / vignetting for systems with rotational symmetry Advanced possibility: - non-sequential component - embedded into sequential optical systems - examples: lightguide, arrays together with focussing optics, beam guiding,... General illumination calculation: - non-sequential raytrace with complete different philosophy of handling - object oriented handling: definition of source, components and detectors 32

33 Relative Illumination Relative illumination or vignetting plot Transmission as a function of the field size Natural and arteficial vignetting are seen relative illumination onset of truncation vignetting natural vignetting cos 4 w total illumination y field in

34 Illumination in Zemax Partly non-sequential raytrace: Choice of surface type non-sequential Non-sequential component editor with many control parameters is used to describe the element: - type of component - reference position - material - geometrical parameters Some parameters are used from the lens data editor too: entrance/exit ports as interface planes to the sequential system parts 34

35 Illumination in Zemax Example: Lens focusses into a rectangular lightpipe 35

36 Illumination in Zemax Complete non-sequential raytrace Switch into a different control mode in File-menue Defining the system in the non-sequential editor, separated into 1. sources 2. light guiding components 3. detectors Various help function are available to constitue the system It is a object (component) oriented philosophy Due to the variety of permutations, the raytrace is slow! 36

37 Illumination in Zemax Many types of components and options are available For every component, several parameters can be fixed: - drawing options - coating, scatter surface - diffraction - ray splitting

38 Illumination in Zemax Starting a run requires several control parameters Rays can be accumulated 38

39 Illumination in Zemax Typical output of a run: 39